对称GaAs/Al0.3Ga0.7As双量子阱中激子的束缚能

在有效质量近似下采用简单的尝试波函数变分地计算了对称GaAs/Al0.3Ga0.7As双量子阱中激子体系束缚能,研究了体系束缚能随阱宽和垒宽的变化情况.发现双量子阱中激子体系束缚能随阱宽变化同单量子阱情况类似,但束缚能的峰值出现在阱宽为10(A)左右,峰值位置小于单阱的情况;束缚能随垒宽的增加有一极小值,这与波函数向垒中的渗透有关.     

核壳结构CdSe/ZnS量子点量子阱中1se1sh 激子光跃迁的受激光子回波研究

在建模和理论分析的基础上, 对三脉冲飞秒激光作用下核壳结构CdSe/ZnS量子点量子阱中1s_e1s_h激子光跃迁引起的受激光子回波效应进行了深入研究.运用有效质量近似方法求解了载流子的静态薛定谔方程,得到能量本征值和对应波函数.基于光学Bloch方程,分析了受激光子回波的参量相关性.结果显示受激光子回波信号可以通过量子点量子阱结构和尺寸的改变进行有效调节.同时,在量子尺寸限制理论的基础上讨论了结构和尺寸的变化对受激光子回波信号的具体影响.     

ZnSe/ZnS抛物量子阱中激子的极化子效应(英文)

采用推广的LLP方法研究了ZnSe/ZnS抛物量子阱中激子的极化子效应。考虑电子和空穴与LO声子的相互作用,得到了激子基态能量和结合能随阱宽的变化关系。结果表明,阱宽较小时,能量随着阱宽的增大而急剧减小;阱宽较大时,能量减小的比较缓慢。和我们以前的工作对比,我们发现ZnSe/ZnS抛物量子阱对激子的束缚强于GaAs/Ga1-xAlxAs抛物量子阱。     

SO和LO声子对GaAs-Ga1-xAlxAs量子阱中激子束缚能的影响

本文考虑了电—声子耦合作用,应用么正变换方法计算了GaAs-Ga1-xAlxAs量子阱中的激子束缚能;得到了激子束缚能随阱宽变化的曲线。当考虑激子声子相互作用后,激子相对于电子极化子和空穴极化子的第一子带底的束缚能小于相应的裸激子的束缚能量。     

纤锌矿InGaN staggered量子阱中的激子态和光学性质

本文将基于有效质量近似下的变分法,理论研究了纤锌矿InGaN/GaN staggered量子阱中的激子态和光学性质.数值结果显示了InGaN量子阱中的量子尺寸和staggered受限垒对束缚于量子阱中的激子态和光学性质有着明显的影响.当阱宽增加时,量子受限效应减弱,激子结合能降低,带间发光波长增加.另一方面,当量子阱中staggered受限势增加时,量子受限效应增强,激子结合能升高,带间发光波长降低.本文的理论结果证明了可以通过调节staggered垒高和量子尺寸来调控纤锌矿InGaN staggered量子阱中的激子态和光学性质.     

外电场对InGaAsP/InP量子阱内激子结合能的影响

在有效质量近似下采用变分法计算了InGaAsP/InP量子阱内不同In组分下的激子结合能,分析了结合能随阱宽和In组分的变化情况,并且讨论了外加电场对激子结合能的影响. 结果表明：激子结合能是阱宽的一个非单调函数,随阱宽的变化呈现先增加后减小的趋势;随着In组分增大,激子结合能达到最大值的阱宽相应变小,这与材料的带隙改变有关;在一定范围内电场的存在对激子结合能的影响很小,但电场强度较大时会破坏激子效应. 关键词： 激子 InGaAsP/InP量子阱 结合能 电场     

非对称方势阱中的激子及其与声子的相互作用

采用类LLP(Lee-Low-Pines)变换和分数维变分法,在讨论有限深非对称方势阱Ga_1－xAl_xAs/ GaAs/Ga_0.7Al_0.3As的分数维基础上,计算了其中激子的基态能量以及声子对其影响,随着势阱宽度增加,激子能量先减小后增大,出现一个最小值.讨论了一侧势垒高度变化对分数维、激子基态能量的影响,并发现声子作用使得激子能量明显增大.另外,非对称方势阱中的激子结合能随阱宽的减小而增     

磁场和量子点尺寸对激子性质的影响

在In_0.6Ga_0.4As/GaAs量子点中,采用一维等效势模型和有限差分法理论计算了激子态的性质,得到了激子跃迁能和束缚能随磁场、横向束缚强度以及量子点尺寸的变化关系.结果表明:加入磁场后,Zeeman效应使得激子的能级简并度解除,激子的基态跃迁能与实验符合得很好;横向束缚强度或磁场强度的增加使得激子的束缚增强;量子点的尺寸对激子的束缚产生重要的影响;通过电子-空穴间平均距离以及激子体系波函数分布图像分析了其产生的物理机制.     

纤锌矿InGaN staggered量子阱中的激子态和光学性质

本文将基于有效质量近似下的变分法,理论研究了纤锌矿InGaN/GaN staggered 量子阱中的激子态和光学性质。数值结果显示了InGaN量子阱中的量子尺寸和staggered受限垒对束缚于量子阱中的激子态和光学性质有着明显地影响。当阱宽增加时,量子受限效应减弱,激子结合能降低, 带间发光波长增加。另一方面,当量子阱中staggered受限势增加时,量子受限效应增强,激子结合能升高,带间发光波长降低。本文的理论结果证明了可以通过调节staggered垒高和量子尺寸来调控纤锌矿InGaN staggered 量子阱中的激子态和光学性质。     

MOCVD生长Ga0.5In0.5P外延层光学性质的研究

本文用光致发光(PL)研究了MOCVD(金属氧化物化学气相沉积)生长的有序Ga_0.5In_0.5P外延层的光学性质.发现有序程度较强的Ga_0.5In_0.5样品的PL谱中一峰的能量随温度升高,先增大而后又减小.根据已有的报道和本文的实验结果,提出了一个有序Ga_0.5In_0.5P的模型,模型中将有序Ga_0.5In_0.5P看作阶宽随机分布的Ⅱ型多量子阱结构,能带边之下存在带尾态,并用该模型对实验结果进行了较好的解释.     

Energy levels of hydrogenic impurity states in GaAs-Ga1−xAlxAs quantum well structures

Binding energies of the ground state and of four excited states of a hydrogenic impurity in quantum well structures consisting of a single slab of GaAs sandwiched between two semi-infinite slabs of Ga_1?xAl_xAs are calculated using a variational approach. The ground-state binding energy is calculated as a function of the barrier potential for a given size of the GaAs quantum well and is found to be linearly dependent on the inverse of the square root of the barrier potential except for very small potentials. The variation of the binding energies of all five states as a function of the size of the GaAs quantum well are also calculated and their behavior is discussed.     

Binding energies of wannier excitons in GaAs-Ga1−xAlxAs quantum well structures

Binding energies of Wannier excitons in a quantum well structure consisting of a single slab of GaAs sandwiched between two semi-infinite slabs of Ga_1?xAl_xAs are calculated using a variational approach. Due to reduction in symmetry along the axis of growth of these quantum well structures and the presence of band discontinuities at the interfaces, the degeneracy of the valence band of GaAs is removed leading to two exciton systems, namely, the heavy hole exciton and the light hole exciton. The variations of the binding energies of these two excitons as a function of the size of the GaAs quantum wells for various values of the heights of the potential barrier are calculated and their behavior is discussed.     

Electronic wavefunctions in asymmetric double quantum well structures studied via spin-flip Raman spectroscopy

Spin-flip Raman spectra have been obtained for two heterostructures, each containing a single CdTe quantum well and a single Cd_1-xMn_xTe quantum well, with barriers of Cd_1-yMn_yTe (y>x). The spectra show a clear sensitivity to the thickness of the central barrier between the two wells. The magnitude of the Raman shifts and the resonance energies help identify the origin of the signals in the structures. When the barrier is broad, two signals are observed, one from each separate well. When the width of the barrier is reduced, a single signal is seen, reflecting the coupling of the electronic states of the two wells. The size of the Raman shifts observed also suggest the presence of a low concentration of donors in the material, which modify the form of the electronic wavefunction in the quantum wells.     

Dependence of the activation energies on the well width in CdTe/ZnTe strained single quantum wells

Photoluminescence (PL) measurements on the CdTe/ZnTe strained single quantum wells grown by using the molecular beam epitaxy technique showed that the sharp excitonic peaks corresponding to the transition from the first electronic subband to the first heavy-hole (E₁–HH₁) were shifted to lower energy with increasing well width. The (E₁–HH₁) interband transitions were calculated by using an envelope function approximation taking into account the strain effects, and the values were in reasonable agreement with those obtained from the (E₁–HH₁) excitonic transitions of the PL spectra. The activation energies of the confined electrons in the CdTe quantum well were obtained from the temperature-dependent PL spectra, and their values increased with increasing CdTe well width due to the quantum confinement effect. The present results can help to improve the understanding of the activation energies dependent on the CdTe well width in CdTe/ZnTe single quantum wells.     

Polaron effects on excitons in parabolic quantum wells: fractional-dimension variational approach

Polaron effects on excitons in parabolic quantum wells are studied theoretically by using a variational approach with the so-called fractional dimension model. The numerical results for the exciton binding energies and longitudinal-optical phonon contributions in GaAs/Al_0.3Ga_0.7As parabolic quantum well structures are obtained as functions of the well width. It is shown that the exciton binding energies are obviously reduced by the electron (hole)-phonon interaction and the polaron effects are un-negligible. The results demonstrate that the fractional-dimension variational theory is effectual in the investigations of excitonic polaron problems in parabolic quantum wells.     

Electron-phonon effects on Stark shifts of excitons in parabolic quantum wells: Fractional-dimension variational approach

Electron-phonon effects on Stark shifts of excitons in parabolic quantum wells are studied theoretically by using a fractional dimension method in combination with a Lee-Low-Pines-like transformation and a perturbation theory. The numerical results for the exciton binding energies and electron-phonon contributions to the binding energies as functions of the well width and the electric field in the Al_0.3Ga_0.7As parabolic quantum well structure are obtained. It is shown that both exciton binding energy and electron-phonon contributions have a maximum with increasing the well width. The binding energy and electron-phonon contribution decrease significantly with increasing the electric-field strength, in special in the wide-well case.     

Polaron in a superlattice with δ-like potentials

The problem of the polaron spectrum is studied in a superlattice having narrow quantum wells and relatively wide potential barriers. A δ-like superlattice potential is chosen to solve the problem. This model is adequate, if the penetration depth of the electron wave function into the barrier region is much greater than the width of the quantum well. A weak-coupling polaron at low temperature is studied. Only volume phonons are considered. Expressions are obtained for the polaron mass and the shift of the polaron energy under these assumptions. To test the model, numerical calculations were performed for an InAs-GaSb superlattice, whose quantum wells are quite deep (the energy offset of the conduction bands in InAs and GaSb equals 830 meV), narrow (the width of a quantum well corresponds to the width of an InAs monolayer 6 Å), and the barrier width corresponding to the thickness of the GaSb layers equals 150 Å. The assumption that the penetration depth of the wave function is much greater than the barrier width holds well.     

Dependence of the electronic parameters on the InyGa1−yAs quantum well width in modulation-doped AlxGa1−xAs/InyGa1−yAs/GaAs strained single quantum wells

The variation of the electronic parameters in the subband as a function of the In_yGa_1−yAs quantum well width in modulation-doped strained Al_xGa_1−xAs/In_yGa_1−yAs/GaAs single quantum wells were investigated by means of Shubnikov-de Haas (S-dH) and Van der Pauw Hall-effect measurements. The fast Fourier transform (FFT) of the S-dH oscillations and the Hall-effect data showed that the carrier density and the mobility of the two-dimensional electron gas (2DEG) occupied in the subband increased as the quantum well width increased. The increase in the 2DEG density with increasing the In_yGa_1−yAs well width originated from an increase in the energy difference between the energy level of the electronic subband and Fermi energy, and the increase in the 2DEG mobility is attributed to a decrease of the scattering source. The electronic subband energies, the corresponding wavefunctions, and the Fermi energies in the Al_xGa_1−xAs/In_yGa_1−yAs/GaAs single quantum wells were calculated by a self-consistent method taking into account the exchange-correlation effect together with the strain and nonparabolicity effects. These results indicate that the electronic parameters in Al_xGa_1−xAs/In_yGa_1−yAs/GaAs strained single quantum wells are significantly dependent on the quantum well width.     

Size dependent effective band gap,optical absorption coefficients and refractive index changes in a wide ZnS/Zn1−xMgxS strained quantum well

Exciton binding energy of a confined heavy hole exciton is investigated in a Zn_1−xMg_xS/ZnS/Zn_1−xMg_xS single strained quantum well with the inclusion of size dependent dielectric function for various Mg content. The effects of interaction between the exciton and the longitudinal optical phonon are brought out. The effect of exciton is described by the effective potential between the electron and hole. The interband emission energy as a function of well width is calculated for various Mg concentration with and without the inclusion of dielectric confinement. Non-linear optical properties are carried out using the compact density matrix approach. The dependence of nonlinear optical processes on the well width is investigated for different Mg concentration. The linear, third order non-linear optical absorption coefficients values and the refractive index changes of the exciton are calculated for different concentration of magnesium content. The results show that the exciton binding energy is found to exceed LO phonon energy of ZnS for x>0.2 and the incorporation of magnesium ions and the effect of phonon have great influence on the optical properties of ZnS/Zn_1−xMg_xS quantum wells.     

Binding energies of donor impurities in modulation-doped double quantum wells under an electric field

In this study, we have investigated theoretically the binding energies of shallow donor impurities in modulation-doped GaAs/Al_0.33Ga_0.67As double quantum wells (DQWs) under an electric field which is applied along the growth direction for different doping concentrations as a function of the impurity position. The electronic structure of modulation-doped DQWs under an electric field has been investigated by using a self-consistent calculation in the effective-mass approximation. The results obtained show that the carrier density and the depth of the quantum wells in semiconductors may be tuned by changing the doping concentration, the electric field and the structure parameters such as the well and barrier widths. This tunability gives a possibility of use in many electronic and optical devices.